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Koala Groups Face Extinction Due to Changing Forests

John Roach
for National Geographic News
April 27, 2007
 
Australia's iconic koalas face an uncertain future as their fragmented habitats shift in response to climate change, fire, and drought, an ecologist said.

For example, St. Bees Island off the coast of Queensland is changing from "a koala-friendly forest to a koala-unfriendly forest," said Alistair Melzer, an ecologist at Central Queensland University (map of Australia).

Melzer has studied koalas for nearly 20 years and the St. Bees Island koalas for 8 years.

Koalas exclusively eat the leaves of eucalyptus trees. There are more than 700 species of eucalyptus, but the marsupials prefer the leaves of only a handful.

As the favored eucalyptus species disappear from the forest, St. Bees Island will eventually become unsuitable for the koalas and the resident population will likely go extinct.

Until recently, the St. Bees population had been considered unusually stable, and was intended to serve as a model for helping struggling populations elsewhere in Australia.

But the island's habitat shift is a new twist for land managers to consider as they set the nation's conservation priorities, Melzer said.

They have to ask, for example, "Do I try to go in there and manage these areas—effectively garden them for koalas or another target species. Or do I simply say, Well, that's life, and let them go?"

Koala Mosaic

As humans settled and sculpted the Australian landscape to fit their needs over the past two centuries, koala habitat has become increasingly fragmented, Melzer said.

(Do you know what habitat you live in? Find out with our guide to Earth's ecosystems.)

"We're seeing, in a lot of cases, where koalas are in preserves of some sort. But the structure and composition of those habitats are changing, simply because that's what forests do," Melzer said.

"Consequently, where you've got a fragmented population, we would expect to see populations disappear over a generation," Melzer added.

In southern Australia a lack of natural controls such as disease or predators allows some isolated populations to grow unchecked, outstripping the landscape, Melzer said.

(Related: "Koalas Overrunning Australia Island 'Ark'" [May 10, 2002].)

In the states of Queensland and New South Wales, however, various populations are decreasing.

"It's happening in a mosaic, in patches of koalas," Melzer said.

"Small populations are contracting and disappearing, so that the extent of the distribution of the species is still pretty good. But the overall distribution is getting thinner and thinner."

Left to fend for themselves, the marsupials may eventually disappear.

The Australian Environment Protection and Biodiversity Conservation Act officially lists koalas as "vulnerable" in New South Wales and southeast Queensland. "Vulnerable" is one step away from "endangered."

Melzer said the entire Australian population should be considered "at risk, however you formally describe that."

Population Control

In addition to the habitat research, Melzer's St. Bees Island koala project aims to identify why the koalas there seem to live in tune with their surroundings while koalas in southern Australia outstrip their habitat.

His postgraduate student Gail Tucker has found that a loss of koala babies just after weaning appears to limit the island's population growth.

While the team is not sure why the young koalas die on St. Bees, the findings do rule out chlamydia as the population-control agent.

The disease causes sterility, so some experts had thought it might regulate koala populations by preventing some females from breeding.

Community members in regions where the animals outstrip the forests have recommended introducing chlamydia to koalas to keep them from having more babies and growing their populations to unsustainable levels.

"All they'll be doing is causing pain and suffering to animals to whom the disease is new," Melzer said.

Deborah Tabart is the chief executive officer of the Australian Koala Foundation in Brisbane.

She said conservation of the species requires a big-picture approach rather than micromanagement of isolated habitats.

The decades of land clearing for farms and houses, damming of rivers, and now the drought and fires have "changed the landscape dramatically," she said.

(See a 2006 photo of farmland devastated by Australia's record drought.)

"We have to change our behavior, the whole world. … We're the ones causing this," she added.

"I feel that when we continually say, Oh, we'll move the koalas [to another habitat], we'll do whatever—I just think that's fiddling while Rome burns."

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